This invention relates to a semiconductor device equipped with a power semiconductor element.
In inverter devices, uninterruptible power supply devices, machining equipments, industrial robots, and other equipments, semiconductor modules which are independent of the main unit of the equipment (general-use modules) are employed.
As semiconductor devices, for example, a metal base plate of prescribed thickness is used as a foundation, and a package equipped with power semiconductor devices is provided on the metal base plate (see Patent Document 1: Japanese Patent Application Publication No. 2003-289130). FIG. 11 is a schematic diagram of a semiconductor device employing a metal base plate as a foundation.
This semiconductor device 100 employs a metal base plate 101 with several millimeters in thickness as a foundation; onto the metal base plate 101 is mounted a metal foil 103 through a solder layer 102. Onto the metal foil 103 is mounted an insulating sheet 104, and onto the insulating sheet 104 are mounted metal foils 105, 106. Further, on the metal foils 105, 106 are mounted semiconductor devices 109, 110 through solder layers 107, 108. Here, the semiconductor devices 109, 110 are, for example, IGBTs (Insulated Gate Bipolar Transistors), FWDs (Free Wheeling Diodes), or other devices. Furthermore, onto the semiconductor devices 109, 110 are mounted heat spreaders 113, 114 through solder layers 111, 112. A resin case 115, molded so as to surround the semiconductor devices 109, 110 and similar, is fixed onto the upper edge of the metal base plate 101. In a hole 117 of the resin case 115, is provided a reinforcement metal ring 118.
Although not shown, metal wires, lead frames, and similar are arranged on the periphery of the semiconductor devices 109 and 110; for example, terminals of the semiconductor devices 109, 110 are electrically bonded to a circuit pattern formed on the insulating sheet 104, or, electrical connections are formed between terminals of the semiconductor devices 109, 110.
Further, the interior of the resin case 115 is filled with a gel 116 comprising a silicone material in order to prevent contact between metal wires and similar, and to protect the semiconductor devices 109, 110, and similar from moisture, humidity, and dust.
Recently, a small-size semiconductor device has been disclosed which does not employ a metal base plate 101 as a foundation (see, for example, Japanese Non-patent Document 1: Komatsu, Soutome and Ikawa, “Small Capacity IGBT Module”, Fuji Jihou, Vol. 78, No. 4, 2005, p. 260 to 263).
FIG. 12 is a schematic diagram of a semiconductor device which does not employ a metal base plate.
In this semiconductor device 200, an insulating sheet 104, metal foil 103 formed on the lower face of the insulating sheet 104, and metal foils 105, 106 formed on the upper face of the insulating sheet 104 serve as the foundation. Semiconductor devices 109, 110 are mounted onto the metal foils 105, 106 through solder layers 107, 108.
In the semiconductor device 200, a resin case 115, molded so as to surround the semiconductor devices 109, 110 and similar, is fixed onto the upper edge of the insulating sheet 104. The interior of the resin case 115 is similarly filled with a gel 116 comprising a silicone material.
By means of such a semiconductor device 200, because a thick metal base plate is not used as a foundation, the semiconductor device can be made lighter in weight, smaller in size, and lower in cost.
Further, as the semiconductor elements 109, 110 mounted within the semiconductor device 100, 200, recently, thin semiconductor elements with reduced turn-off losses have been used (see, for example, Japanese Non-patent Document 2: Miyashita, “U series IGBT modules”), Fuji Jiho, Vol. 77, No. 5, 2004, p. 313 to 316).
For example, conventionally, PT (Punch Through) type semiconductor elements, having a thickness of approximately 350 μm and fabricated using epitaxial silicon substrates, have been mainly used. Recently, however, the use of NPT (Non-Punch Through) semiconductor elements having a thickness of approximately 100 μm and fabricated using FZ (Floating Zone) substrates has become popular.
However, if the semiconductor devices 100, 200 described above are repeatedly operated, because the thickness of the mounted semiconductor elements 109, 110 is 100 μm or greater, heat generation and dissipation by the semiconductor elements 109, 110 causes substantially expansion of the semiconductor elements 109, 110. As a result, excessive amount of stress repeatedly occurs between the semiconductor elements 109, 110 and the solder layers 107, 108 below the semiconductor elements 109, 110.
If such semiconductor devices 100, 200 are operated over extended periods of time, the adhesive forces between the semiconductor elements 109, 110 and the solder layers 107, 108 cannot withstand the stress, and peeling occurs at the interface between the semiconductor elements 109, 110 and the solder layers 107, 108 to cause wire breakage. Consequently, there is a problem that reliability of the semiconductor device is undermined.
This invention has been made in light of the above circumstances, and has as an object to provide a semiconductor device with excellent reliability even when used over extended period of time, as well as a method for manufacturing such a semiconductor device.
Further objects and advantages of the invention will be apparent from the following description of the invention.